When you consider that the global commercial shipping industry consuming 400 million tonnes of fuel per year and producing 1.2 billion tonnes of carbon dioxide per year, it almost seems to become a matter of just how many zeros are there.
With such large numbers, a small percentage can represent considerable improvement. When a ship enters a country's territorial waters, as part of the standard pratique, the Bio-fouling Record Book that has been discussed by various authorities including the IMO, should be presented as a mandatory requirement.
This makes sense for the environment but also for the ship owner. The cost to the ship owner to keep their hulls free of unacceptable levels of growth and the consequential reduction in greenhouse gasses would be more than compensated by the savings in fuel consumption and future carbon tax credits. There is the added benefit of reducing the risk of introducing foreign marine pests into the local marine environment.
Marintek has monitored the fuel consumption and hull performance of more than one hundred ships over a period of ten to 20 years. It has been observed that speed reductions of five and ten percent are typical between hull renewals when the hull renewal period is three to five years.
According to CE Delft, a speed reduction of ten percent due to fouling would roughly correspond to an increase in fuel consumption of 30 percent.
Meanwhile, according to the Surface Ship Hull and Propeller Fouling Management and Michael Walker, of the Sea Systems Group, UK Ministry of Defence, the fouling extent by area of wetted hull of 100 percent coverage of slime and occasional patches of weed give an Increase in friction coefficient of 20 percent and an increase in fuel consumption of twelve percent.
Taking these facts into account the results are considerable. A Panamax-sized ship will consume an extra 36 tonnes of fuel per day at design speed and draught, or a loss of approximately 1.5 knots, costing US$16,000 and producing an additional 115 tons of carbon dioxide per day.
With environmentally acceptable technology available like hull surface treatment, (HST), currently only available in Australia, where it is possible to treat a ships hull whilst alongside in less than 16 hours without divers there is no reason for ship owners to tolerate these penalties.
HST is a passive treatment and does not damage the underwater coatings or remove any growth. The growth is killed using thermal shock and is then polished off over the following three to four weeks by the hydraulic action of waves and the vessel's movement through the water.
Chris Geater